This page contains answers to common problems about
Microsoft Outlook duplicates, where they come from, and how to avoid them. All of the information
contained pertains to Microsoft Outlook, not Outlook Express. To find out more, including the differences between
Outlook and Outlook Express and how to find out which one you use, see our
general FAQ.

This page is broken up into two parts, how to prevent the duplicates from occurring in the first place and how to clean up the duplicates.

Prevention

Many things cause duplicates to appear, including synchronization with Palms, Blackberrys, or Pocket PC PDAs, restoring Exchange public folders from backups, using Netfolders, incorrect Outlook rules and many other reasons. Preventing them from occurring in the future is the first step to eradicating them.

There are a few things you can check to stop duplicate email messages.

Start by checking Rules to be sure that copies are not being made to the Inbox, and make sure that all your rules end in "Stop Processing" actions.

Then check the task manager to be sure that there is only one instace of Outlook running. Two instances of outlook.exe running can produce two messages arriving at the same time. You will need to then determine why two instances of Outlook were running in the first place.

Another thing you can do is to delete/remove ALL your e-mail accounts and recreate them. This worked for some people.

Also, if your running Outlook XP, be sure that you are at service pack 2 or later. You can tell if you need to upgrade at Microsoft Product Updates.

Finally, another person had this happen when he had two e-mail accounts set up - using two e-mail addresses, but the same POP3 incoming and same SMTP outgoing. What happened is that the second account was getting the e-mails from the POP3 server before they were actually deleted after the first account was finished. If this is the problem you can disable the receive on the second account. There is a Microsoft article explaining the problem more thoroughly at http://support.microsoft.com/?kbid=284404.

Sending multiple email messages can be the result of Norton Anti-Virus and Outlook combined. Apparently when Norton
scans outgoing emails it may send it out twice. The quick fix is to change the Norton properties to not scan outgoing
messages, but you may want to consult the Symantec Knowledge Base about your software.

What you may be seeing is an entry for an email
address and one for business fax numbers. This is because Outlook considers fax
numbers as "valid transport addresses". You can prevent these duplicate names
from appearing by prepending "Fax:" before the number in the contact. This has the effect of
preventing Outlook from seeing the fax number as a valid transport address, so you
only get one name (the email address). This technique is useful...

[Editor's note: Shameless self promotion warning]
...if you have too many contacts to process, and you can either export them all to Excel,
change the numbers, then import them back, or you can use our Hide Fax Numbers
add-in to process them all. The add-in has recently been updated to automatically process
the fax numbers in contacts as you add them.

In addition, there may be other solutions that exist. See the Resources
page for more information about these solutions.

Check to see if you have more than one Outlook running. Having more than one Outlook
process running while synchronizing can lead to duplicate appointments. To see if you
have more than one running, quit Outlook, open the Task Manager and go to the processes tab.
Once there, click once on the "Name" column to sort alphabetically, then look for "Outlook.exe".
If it's listed there, then highlight it and click on "End Process". Some people report finding
up to four copies of Outlook running using this method. You should be able to
resume your synchronization after performing this step.

If you have just a few duplicates, it may be easiest to
manually remove them. For emails, this is no problem but for any other Outlook item it
is easiest to view the items in a table view, then select the duplicates, then delete them.

To accomplish this, go to View...By Category (or "By" anything really). This gets the view
into a mode you can work with. Click either names or subjects (or any shown field)
in the column header (in the gray area) to gather similar items together. You can then delete
all the duplicates you find.

[Editor's note: Another shameless self promotion warning]
Sperry Software offers 8 different Outlook duplicate eliminators, including a
bundle package comprising all 8 for one price.
We are aware of cheaper and sometimes free solutions to resolve duplicates (see
the Resources page). However, it is our hope that
you will support us by purchasing our products so that we can continue to maintain
useful pages like this one.

2) Close Outlook, then right click Outlook Icon on the desktop. Select Properties, select Data Files. Remove the links to the backup .pst file.

3) Under the folder named HKEY_CURRENT_USER\Software\Microsoft\Windows
Messaging Subsystem\Profiles\Microsoft Outlook Internet Settings you will
have a series of folders with long hexadecimal numbers. Two of the folder
will point to your *.pst file. You will next to export one of them
(Registry | Export registry) and then delete the exported hexadecimal
folder. Start Outlook, if it is fubar. Close outlook and import the
registry file you just exported. Export the other hexadecimal folder and
delete it. Start Outlook again.

Now you can start Outlook. Outlook will start like it is in a first run
condition and you will have to open your old *.pst file via a File | Open |
Personal Folders. Select View | Folder List. Right click on Personal
Folders (the one that doesn't have Outlook Today next to it) and select
properties. Near the bottom is a checkbox to have mail delivered to this
set of folders, check it. Restart Outlook and you're all set.

In Tools...Addressbook you may have to pick from a list that looks like this:

Outlook Address Book
Contacts
Contacts
Contacts
Contacts

Where only the last one has any contacts.

The way to remove this condition is to go to Tools...Email Accounts...Directories...View or Change.
Select your Outlook Address Book service, then change. On the next page, delete the first 3
contacts folders that appear. Close and restart Outlook and they should be gone.

Netfolders has been known to cause bugs and the feature has been taken out of Microsoft Outlook 2002. The only suggestion received so far has been to try deleting the net folders share and recreating it.

Sperry Software would like to thank these Outlook MVPs without whom this page would not exist. In case you don't know, MVPs are volunteers that spend time on various newsgroups, forums and web sites donating their time and knowledge to helping people overcome their difficulties with Outlook.